This invention relates to metal silicide targets for sputtering and a method of manufacturing the same whereby the formation of particulate matters, or particles, can be substantially decreased from the prior art level and an increase in the oxygen content due to fine grinding of the powder material is avoided. The metal silicide films formed by sputtering process from the metal silicide targets of the invention are useful for the films of large-scale integrated circuits that involve very fine wiring and interconnecting line widths and spaces. They promise use in present and future semiconductor devices such as high integration-scale (e.g., 4, 16, and 64-megabit) LSIs and VLSIs.
Polysilicon has hitherto been used in electrodes or wiring or interconnecting lines of LSI semiconductor devices. The tendency toward greater complexity of LSI semiconductor devices has caused it to present the problem of delay in signal transmission rate due to its resistance. Meanwhile, there is a demand for higher-melting-point materials to be used as electrodes to facilitate the formation of lines by self-alignment technique. Under these circumstances, wiring and electrodes of metal silicides that possess lower electric resistivity than polysilicon and are compatible with the silicon gate process have come into use. Examples of the metal silicides are as follows: tungsten silicides (WSi.sub.x), molybdenum silicides (MoSi.sub.x), tantalum silicides (TaSi.sub.x), titanium silicides (TiSi.sub.x), cobalt silicides (CoSi.sub.x), chromium silicides (CrSi.sub.x), nickel silicides (NiSi.sub.x), and silicides of platinum metals, etc. A film of such a metal silicide is formed by sputtering of a metal silicide target. The metal silicide target used often has a silicon/metal molar ratio greatly in excess of 2, because a molar ratio x of less than 2 imposes so much stresses on the resulting film that the film tends to come off.
Metal silicide targets are manufactured by mixing silicon powder and metal powder in a silicon/metal molar ratio of 2 or more, forming the mixture into a synthesized silicide powder, compressing and sintering the powder to obtain compacts, and then machining the sintered compacts to a desired shape.
The recent trend toward greater scale of integration of LSI semiconductor devices (e.g., to 4, 16, and 64-megabits) has reduced their wiring line widths to submicron levels. With this tendency, "particles" originating from the target are attracting attention as a subject of growing concern. The term "particles" as used herein means the particulate matter that is scattered and flies off from a target on sputtering of the target. The particles deposit directly on the film on a substrate or stick and build up on surrounding walls and parts and then come off to deposit on the film, inviting severe troubles such as breaking and shorting of lines. The particle problem is becoming more and more serious with the progress of integration and refinement of the circuits of electronic devices. Thus it is noted anew that conventional silicide targets are unsuitable for VLSI applications because they emit too many particles during sputtering.
It has already been recognized in the art that the presence of coarse aggregates of free silicon phases contribute largely to the release of particles from metallic silicide targets. On the basis of this recognition, e.g., Japanese Patent Application Public Disclosure No. 191366/1992 discloses a metal silicide target of a refractory metal and Si characterized in that the average diameter of free Si particles is 30 .mu.m or less and the number of free Si particles having diameters of 40 .mu.m or more that appear on the surface and cross section of the target is 50 or less per square millimeter, and also a method of manufacturing the target. Patent Application Public Disclosure No. 1370/1993 previously filed by the present applicant imposes an additional restriction, introducing a metal silicide target characterized in that the number of coarse silicon phases 10 .mu.m or larger in size that are found present in the sputter surface of the target is 10 or fewer per square millimeter. Also No. 1370/1993 provides after a method of manufacturing such targets.
For the manufacture of metal silicide targets with fewer coarse silicon phases, finer raw material silicon and metal powders are used. Here arises another problem; the finer the powders the higher the oxygen content. Oxygen-rich silicide targets give off oxygen on sputtering, which is detrimental to the properties, such as resistivity, of the resulting film.